It is known that in many industrial processes it is necessary to control the flow of process gases. In the manufacture of semiconductor devices such as integrated circuits the process gases used must be of high purity and must be particle free. With the ever increasing density of circuit components on semiconductor "chips" it is increasingly necessary to reduce contamination levels of these process gases.
Unfortunately one source of particle cotamination of the process gases comes from the gas delivery or control assembly itself. There are two main types of gas delivery assemblies, industrially known as valves, which are used to open or close the gas flows during semiconductor device manufacture. The first type uses a diaphragm to interrupt the gas flow but this requires the use of non-linear gas flows which can cause turbulence provoking the production of small particles and causing undesired pressure drops across the delivery assembly. A second type of gas delivery assembly has a "straight through" gas flow and uses a bellows assembly incorporating a translation means and a seat seal to open or close the gas flow. While this second type of gas delivery assembly solves the problems caused by excessive pressure drops, it suffers from several drawbacks.
A bellows configuration has an undulating surface and therefore a large surface area which can act as a source of particles.
Furthermore, movement of the bellows during opening and closing of the gas delivery assembly can create additional particles due to deformation of its surface.
If the bellows assembly is made longer, less relative movement is required to open and close the gas flow. However the surface area of the bellows is increased thus increasing the possibility of loose particle production. Furthermore the walls of the bellows enclosure area are increased again increasing the probability of loose particle production. In addition this increases the dead volume exposed to the gas flow and hence increases the risk of turbulence. This turbulence itself can provoke increased particle production and also create an increased pressure drop across the gas delivery assembly.
Prior art gas delivery assemblies are difficult to purge efficiently to remove particles.
It is therefore an object of the present invention to provide a high purity gas delivery control assembly free from one or more of the defects of prior art gas delivery control assemblies.
Another object of the present invention is to provide a high purity gas delivery control assembly free from the introduction of particles into the gas flow.
It is another object of the present invention to provide a high purity gas delivery control assembly easy to purge.
It is yet another object of the present invention to provide a high purity gas delivery control assembly having only a very small dead volume.
Additional objects and advantages of the high purity gases delivery control assemblies of the present invention will become apparent to those skilled in the art by reference to the following detailed description thereof and drawings wherein: